In a sealing device provided as a means for axially sealing a crank shaft of an engine, as a sealing device provided in parallel with a magnetic type rotary encoder for detecting a rotation of the engine, there has been conventionally known a structure, for example, disclosed in Japanese Unexamined Patent Publication No. 2004-93554, patent document 1.
In other words, the sealing device is supported to an inner periphery of a non-rotating housing, and is brought into slidable contact with an outer peripheral surface of a crank shaft. A pulsar ring (a pulsar wheel) magnetized in multiple poles in a circumferential direction is attached to a shaft end of the crank shaft, and a magnetic sensor facing to the pulsar ring from an outer peripheral side is attached to the housing so as to be adjacent to the sealing device in an axial direction. The magnetic sensor structures a magnetic type rotary encoder together with the pulsar ring, generates a pulse in correspondence to a change of a magnetic field of the pulsar ring rotating together with the crank shaft, and detects the rotation of the crank shaft.
However, in accordance with the prior art described in the patent document 1 mentioned above, since a sensor and a shaft seal ring are attached to the housing side by side in the axial direction, a dimension in an axial direction of the housing (for example, an engine block) becomes large, and a mounting structure is entirely complicated.